From 41964648eea1427d53934b886abb68cc8457b019 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Tue, 8 Sep 2015 12:41:05 -0300
Subject: long strings are created directly in final position when possible
 (instead of using an auxiliar buffer to first create the string and then
 allocate the final string and copy result there)

---
 lvm.c | 41 ++++++++++++++++++++++++++---------------
 1 file changed, 26 insertions(+), 15 deletions(-)

(limited to 'lvm.c')

diff --git a/lvm.c b/lvm.c
index 6a6710b3..59f36e3a 100644
--- a/lvm.c
+++ b/lvm.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.c,v 2.249 2015/08/03 19:50:49 roberto Exp roberto $
+** $Id: lvm.c,v 2.250 2015/08/03 20:40:26 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -445,6 +445,17 @@ int luaV_equalobj (lua_State *L, const TValue *t1, const TValue *t2) {
 
 #define isemptystr(o)	(ttisshrstring(o) && tsvalue(o)->shrlen == 0)
 
+/* copy strings in stack from top - n up to top - 1 to buffer */
+static void copy2buff (StkId top, int n, char *buff) {
+  size_t tl = 0;  /* size already copied */
+  do {
+    size_t l = vslen(top - n);  /* length of string being copied */
+    memcpy(buff + tl, svalue(top - n), l * sizeof(char));
+    tl += l;
+  } while (--n > 0);
+}
+
+
 /*
 ** Main operation for concatenation: concat 'total' values in the stack,
 ** from 'L->top - total' up to 'L->top - 1'.
@@ -464,24 +475,24 @@ void luaV_concat (lua_State *L, int total) {
     else {
       /* at least two non-empty string values; get as many as possible */
       size_t tl = vslen(top - 1);
-      char *buffer;
-      int i;
-      /* collect total length */
-      for (i = 1; i < total && tostring(L, top-i-1); i++) {
-        size_t l = vslen(top - i - 1);
+      TString *ts;
+      /* collect total length and number of strings */
+      for (n = 1; n < total && tostring(L, top - n - 1); n++) {
+        size_t l = vslen(top - n - 1);
         if (l >= (MAX_SIZE/sizeof(char)) - tl)
           luaG_runerror(L, "string length overflow");
         tl += l;
       }
-      buffer = luaZ_openspace(L, &G(L)->buff, tl);
-      tl = 0;
-      n = i;
-      do {  /* copy all strings to buffer */
-        size_t l = vslen(top - i);
-        memcpy(buffer+tl, svalue(top-i), l * sizeof(char));
-        tl += l;
-      } while (--i > 0);
-      setsvalue2s(L, top-n, luaS_newlstr(L, buffer, tl));  /* create result */
+      if (tl <= LUAI_MAXSHORTLEN) {  /* is result a short string? */
+        char buff[LUAI_MAXSHORTLEN];
+        copy2buff(top, n, buff);  /* copy strings to buffer */
+        ts = luaS_newlstr(L, buff, tl);
+      }
+      else {  /* long string; copy strings directly to final result */
+        ts = luaS_createlngstrobj(L, tl);
+        copy2buff(top, n, getaddrstr(ts));
+      }
+      setsvalue2s(L, top - n, ts);  /* create result */
     }
     total -= n-1;  /* got 'n' strings to create 1 new */
     L->top -= n-1;  /* popped 'n' strings and pushed one */
-- 
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